Engineered-phosphor LED packages and related methods

ABSTRACT

In accordance with certain embodiments, a phosphor element at least partially surrounding a light-emitting die is shaped to influence color-temperature divergence.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.13/828,498, filed Mar. 14, 2013, the entire disclosure of which isincorporated by reference herein.

FIELD OF THE INVENTION

In various embodiments, the present invention generally relates tolight-emitting diodes (LEDs) and, in particular, to LED dies packagedwith engineered phosphor layers and lighting systems incorporating suchLED dies.

BACKGROUND

An increasing number of light fixtures utilize LEDs as light sources dueto their lower energy consumption, smaller size, improved robustness,and longer operational lifetime relative to conventional filament-basedlight sources. Conventional LEDs emit quasi-monochromatic radiationranging from infrared through the visible spectrum to ultraviolet.Conventional LEDs emit light at a particular wavelength, ranging from,for example, red to blue or ultraviolet (UV) light. However, forpurposes of general illumination, the relatively narrow spectral widthof light emitted light by LEDs is generally converted to broad-spectrumwhite light.

Traditionally, there are two ways of obtaining white light from LEDs.One approach utilizes two or more LEDs operating at differentwavelengths, where the different wavelengths are chosen such that theircombination appears white to the human eye. For example, one may useLEDs emitting in the red, green, and blue wavelength ranges. Such anarrangement typically requires careful control of the operating currentsof each LED, such that the resulting combination of wavelengths isstable over time and different operating conditions, for exampletemperature. Because the different LEDs may be formed from differentmaterials, different operating parameters may be required for thedifferent LEDs; this complicates the LED circuit design. Furthermore,such systems typically require some form of light combiner, diffuser ormixing chamber, so that the eye sees white light rather than thedistinct colors of each of the different LEDs. Such light-mixing systemstypically add cost and bulk to lighting systems and may reduce theirefficiency.

White light may also be produced in LED-based systems for generalillumination via the utilization of wavelength-conversion materials(also called light-conversion materials) such as phosphors, sometimescalled phosphor-converted LEDs. For example, an LED combined with awavelength-conversion material generates white light by combining theshort-wavelength radiant flux (e.g., blue light) emitted by thesemiconductor LED with long-wavelength radiant flux (e.g., yellow light)emitted by the wavelength conversion material. The chromaticity (orcolor), color temperature, and color-rendering index are determined bythe relative intensities of the component colors. For example, the lightcolor may be adjusted from “warm white” with a correlated colortemperature (CCT) of 2700 Kelvin or lower to “cool white” with a CCT of6500 Kelvin or greater by varying the type or amount of phosphormaterial. White light may also be generated solely or substantially onlyby the light emitted by the one or more wavelength conversion materials.

In isolation, bare LED dies generally exhibit a Lambertian luminousintensity distribution pattern, as shown in FIG. 1A, that is aconsequence of the light being uniformly emitted from a planar surface.(That is, the projected area of its light-emitting region decreasesaccording to the cosine of the viewing angle with respect to the surfacenormal.)

The wavelength-conversion material is generally one or more phosphorparticles. Such particles emit with a substantially isotropicdistribution. In a phosphor-converted LED, the phosphor particles aregenerally embedded into a transparent matrix, for example a silicone,and typically have a substantially hemispherical shape surrounding thedie with the die positioned at the equator and in the center of thehemisphere. The hemispherical shape is used because it generally resultsin relatively high light extraction efficiency because of reduced totalinternal reflection (TIR) at the phosphor/air interface. The intensitydistribution of isotropic emitting phosphor particles in a hemisphericaltransparent matrix is shown in FIG. 1B.

As may be seen by comparing FIGS. 1A and 1B, the intensity distributionsof a bare-die LED and embedded phosphor particles are different. Thisdifference results in the chromaticity of the combined light varyingwith viewing angle, resulting in a non-uniform color distribution asseen by the human eye. For example, a phosphor-coated blue LED may betypically perceived as being cool white when viewed head-on, but warmwhite when viewed obliquely. Thus, while the hemispherical shapeprovides relatively high efficiency, it suffers from relatively poorcolor temperature uniformity with angle.

In order to mitigate the relatively poor angular color uniformity ofconventional phosphor-converted LEDs, illumination systems incorporatingsuch phosphor-converted LEDs often require additional elements, such asdiffusers, mixing chambers, or the like, to homogenize the colorcharacteristics. Such homogenization often degrades the light-intensitydistribution pattern, however, resulting in the need for secondaryoptics to attempt to re-establish the desired light-intensitydistribution pattern. The addition of these elements typically requiresundesirable additional space or volume, adds cost and expense, andreduces output efficiency.

Accordingly, there is a need for structures, systems and proceduresenabling LED-based illumination systems to generate uniform colordistribution of emitted light and operate with high extractionefficiency while utilizing low-cost integration of phosphors with theLEDs.

SUMMARY

In accordance with certain embodiments, one or more phosphor elements atleast partially surrounding a light-emitting element (LEE) are shaped toimprove uniformity of chromaticity of light emitted from the LEE as afunction of viewing angle. The phosphor element may be formed of asingle structure or multiple discrete portions that may be opticallycoupled and at least a portion of the surface of the phosphor elementmay be roughened (i.e., textured) to improve light-extraction efficiencyfrom the device. Various embodiments of this invention engineer (1) theangular intensity distribution of the light emitted from the LEE as itexits the surrounding phosphor and (2) the angular intensitydistribution of light emitted from the phosphor to achieve a desiredangular characteristic of one or more optical parameters, for example toachieve a relatively uniform color temperature with viewing angle.

As utilized herein, the term “light-emitting element” (LEE) refers toany device that emits electromagnetic radiation within a wavelengthregime of interest, for example, visible, infrared or ultravioletregime, when activated, by applying a potential difference across thedevice or passing a current through the device. Examples of LEEs includesolid-state, organic, polymer, phosphor-coated or high-flux LEDs,microLEDs (described below), laser diodes or other similar devices aswould be readily understood. The emitted radiation of a LEE may bevisible, such as red, blue or green, or invisible, such as infrared orultraviolet. A LEE may produce radiation of a spread of wavelengths. ALEE may feature a phosphorescent or fluorescent material for convertinga portion of its emissions from one set of wavelengths to another. A LEEmay include multiple LEEs, each emitting essentially the same ordifferent wavelengths. In some embodiments, a LEE is an LED that mayfeature a reflector over all or a portion of its surface upon whichelectrical contacts are positioned. The reflector may also be formedover all or a portion of the contacts themselves. In some embodiments,the contacts are themselves reflective.

A LEE may be of any size. In some embodiments, a LEE has one lateraldimension less than 500 μm, while in other embodiments a LEE has onelateral dimension greater than 500 um. Exemplary sizes of a relativelysmall LEE may include about 175 μm by about 250 μm, about 250 μm byabout 400 μm, about 250 μm by about 300 μm, or about 225 μm by about 175μm. Exemplary sizes of a relatively large LEE may include about 1000 μmby about 1000 μm, about 500 μm by about 500 μm, about 250 μm by about600 μm, or about 1500 μm by about 1500 μm. In some embodiments, a LEEincludes or consists essentially of a small LED die, also referred to asa “microLED.” A microLED generally has one lateral dimension less thanabout 300 μm. In some embodiments, the LEE has one lateral dimensionless than about 200 μm or even less than about 100 μm. For example, amicroLED may have a size of about 225 μm by about 175 μm or about 150 μmby about 100 μm or about 150 μm by about 50 μm. In some embodiments, thesurface area of the top surface of a microLED is less than 50,000 μm² orless than 10,000 μm². The size of the LEE is not a limitation of thepresent invention, and in other embodiments the LEE may be relativelylarger, e.g., the LEE may have one lateral dimension on the order of atleast about 1000 μm or at least about 3000 μm.

As used herein, “phosphor” refers to any material that shifts thewavelengths of light irradiating it and/or that is fluorescent and/orphosphorescent, and is utilized interchangeably with the term“light-conversion material” or “phosphor-conversion element.” As usedherein, a “phosphor” may refer to only the powder or particles (of oneor more different types) or to the powder or particles with the binder.The light-conversion material is incorporated to shift one or morewavelengths of at least a portion of the light emitted by LEEs to otherdesired wavelengths (which are then emitted from the larger device aloneor color-mixed with another portion of the original light emitted by thedie). A light-conversion material may include or consist essentially ofphosphor powders, quantum dots, organic dye or the like within atransparent matrix. Phosphors are typically available in the form ofpowders or particles, and in such case may be mixed in binders. Anexemplary binder is silicone, i.e., polyorganosiloxane, which is mostcommonly polydimethylsiloxane (PDMS). Phosphors vary in composition, andmay include lutetium aluminum garnet (LuAG or GAL), yttrium aluminumgarnet (YAG) or other phosphors known in the art. GAL, LuAG, YAG andother materials may be doped with various materials including forexample Ce, Eu, etc. The specific components and/or formulation of thephosphor and/or matrix material are not limitations of the presentinvention. As used herein, a “phosphor chip” is a discrete piece orlayer of phosphor that has been fabricated and cured while unattached toany LEE, and that may be later coupled to an LEE by, e.g., opticalbonding or via an optical adhesive.

The binder may also be referred to as an encapsulant or a matrixmaterial. In one embodiment, the binder includes or consists essentiallyof a transparent material, for example silicone-based materials orepoxy, having an index of refraction greater than 1.35. In oneembodiment the phosphor includes or consists essentially of othermaterials, for example fumed silica or alumina, to achieve otherproperties, for example to scatter light, or to reduce settling of thepowder in the binder. An example of the binder material includesmaterials from the ASP series of silicone phenyls manufactured by ShinEtsu, or the Sylgard series manufactured by Dow Corning.

Herein, two components such as light-emitting elements, opticalelements, and/or phosphor chips being “aligned” or “associated” witheach other may refer to such components being mechanically and/oroptically aligned. By “mechanically aligned” is meant coaxial orsituated along a parallel axis. By “optically aligned” is meant that atleast some light (or other electromagnetic signal) emitted by or passingthrough one component passes through and/or is emitted by the other.

In an aspect, embodiments of the invention feature a light emittingdevice that includes or consists essentially of a light-emitting diehaving (i) a top face and a bottom face opposite the top face, the topand/or bottom face being configured for emission of light therefrom, and(ii) a sidewall spanning the top and bottom faces, and at leastpartially surrounding the light-emitting die, a phosphor elementincluding or consisting essentially of (i) a binder and (ii) disposedwithin the binder, one or more wavelength-conversion materials forabsorbing at least a portion of light emitted from the light-emittingdie and emitting converted light having a different wavelength. Thephosphor element has an outer contour having a curved region thatdefines only a portion of a hemisphere having a hemisphere radius, and aplanar base of the phosphor element has a non-zero centroid z-offsetwithin the hemisphere.

Embodiments of the invention may include one or more of the following inany of a variety of different combinations. The ratio of the centroidz-offset to the hemisphere radius may be a value ranging from 0.3 to0.8. The bottom face of the light-emitting die may be substantiallycoplanar with the base of the phosphor element. The ratio of thecentroid z-offset to the hemisphere radius may be a value ranging from0.5 to 0.77. The ratio of the centroid z-offset to the hemisphere radiusmay be a value ranging from 0.3 to 0.5. The outer contour of thephosphor element may have a planar region disposed over thelight-emitting die and substantially parallel to the top face of thelight-emitting die. The ratio of a z-offset value of the planar regionwithin the hemisphere to the hemisphere radius may have a value rangingfrom 0.02 to 0.15. The ratio of a z-offset value of the planar regionwithin the hemisphere to the hemisphere radius may have a value rangingfrom 0.04 to 0.12. The radius (or other lateral dimension such as width)of the planar region may be a value ranging from 50 μm to 1000 μm. Theradius (or other lateral dimension such as width) of the planar regionmay be a value ranging from 200 μm to 800 μm. The ratio of the centroidz-offset to the hemisphere radius may be approximately defined by−1.9×F+0.67, where F is a ratio of the z-offset value of the planarregion within the hemisphere to the hemisphere radius. The centroidz-offset value may be approximately defined by 1.41×R−0.8, where R isthe hemisphere radius.

The hemisphere radius may be a value ranging from about 0.2 mm to about20 mm. The hemisphere radius may be a value ranging from about 0.5 mm toabout 5 mm. The hemisphere radius may be a value ranging from about 0.7mm to about 1.5 mm. The base radius (or width) of the phosphor elementmay be a value ranging from 0.6 mm and 1.0 mm. The outer contour of thephosphor element may have a planar region disposed over thelight-emitting die and substantially parallel to the top face of thelight-emitting die. The radius (or width) of the planar region may be avalue ranging from about 0.15 mm to about 0.45 mm. The height (distance)from the base of the phosphor element to the planar region may be avalue ranging from about 0.15 mm to about 0.5 mm. The outer contour ofthe phosphor element may have a region defined by a cylindrical cutoffwithin the hemisphere. The ratio of the length (e.g., dimension parallelto the base of the phosphor element and/or bottom face of thelight-emitting die) of the cylindrical cutoff to the hemisphere radiusmay be a value ranging from 0.75 to 0.95. The length of the cylindricalcutoff may be a value ranging from 50 μm to 500 μm.

Light emitted from the light-emitting die may have a Lambertiandistribution. The converted light may have an isotropic distribution.The converted light may combine with unconverted light emitted from thelight-emitting die to form substantially white light. The divergence ofcolor temperature of the substantially white light emitted from thedevice may vary, over an angular range of 0° to 85°, no more than 0.01in terms of Δu′v′ deviation from a spatially weighted averagedchromaticity. The divergence of color temperature of the substantiallywhite light emitted from the device may vary, over an angular range of0° to 85°, no more than 0.005 in terms of Δu′v′ deviation from aspatially weighted averaged chromaticity. The one or more wavelengthconversion materials may include or consist essentially of one or morephosphor particles. The phosphor particles may each include or consistessentially of garnet and a rare-earth element. The device may include,disposed beneath (i) at least a portion of the light-emitting die and/or(ii) the phosphor element, a mounting surface reflective to convertedlight and/or unconverted light emitted from the light-emitting die. Themounting surface may have a reflectivity to visible light ofapproximately 95% to approximately 98%. At least a portion of the outercontour of the phosphor element may have a surface texture for reducingtotal internal reflection. The light-emitting die may be a barelight-emitting diode die. The light-emitting die may include or consistessentially of a GaN-based semiconductor material (e.g., a materialincluding GaN, AlN, and/or InN and/or combinations or alloys thereof).The semiconductor material may include In. The light-emitting die mayemit blue and/or ultraviolet light.

In another aspect, embodiments of the invention feature a light-emittingdevice that includes or consists essentially of a light-emitting diehaving (i) a top face and a bottom face opposite the top face, the topand/or bottom face being configured for emission of light therefrom, and(ii) a sidewall spanning the top and bottom faces, and at leastpartially surrounding the light-emitting die, a phosphor elementincluding or consisting essentially of (i) a binder and (ii) disposedwithin the binder, one or more wavelength-conversion materials forabsorbing at least a portion of light emitted from the light-emittingdie and emitting converted light having a different wavelength. Thephosphor element has an outer contour having (i) a curved region thatdefines only a portion of a hemisphere having a hemisphere radius and(ii) a planar region disposed over the light-emitting die andsubstantially parallel to the top face of the light-emitting die.

Embodiments of the invention may include one or more of the following inany of a variety of different combinations. The bottom face of thelight-emitting die may be substantially coplanar with a base of phosphorelement opposite the planar region. The ratio of a z-offset of theplanar region within the hemisphere to the hemisphere radius may be avalue ranging from 0.02 to 0.15. The ratio of a z-offset of the planarregion within the hemisphere to the hemisphere radius may be a valueranging from 0.04 to 0.12. The outer contour of the phosphor element mayhave a region defined by a cylindrical cutoff within the hemisphere. Theratio of a length of the cylindrical cutoff to the hemisphere radius maybe a value ranging from 0.75 to 0.95. The length of the cylindricalcutoff may be a value ranging from 50 μm to 500 μm. The length of thecylindrical cutoff may be a value ranging from about 0.2 mm to about 20mm. The hemisphere radius may be a value ranging from about 0.7 mm toabout 5 mm. Light emitted from the light-emitting die may have aLambertian distribution. The converted light may have an isotropicdistribution. The converted light may combine with unconverted lightemitted from the light-emitting die to form substantially white light.

The divergence of color temperature of the substantially white lightemitted from the device may vary, over an angular range of 0° to 85°, nomore than 0.01 in terms of Δu′v′ deviation from a spatially weightedaveraged chromaticity. The divergence of color temperature of thesubstantially white light emitted from the device may vary, over anangular range of 0° to 85°, no more than 0.005 in terms of Δu′v′deviation from a spatially weighted averaged chromaticity.

The one or more wavelength conversion materials may include or consistessentially of one or more phosphor particles. The phosphor particleseach may include or consist essentially of garnet and a rare-earthelement. The light-emitting device may include, disposed beneath (i) atleast a portion of the light-emitting die and/or (ii) the phosphorelement, a mounting surface reflective to converted light and/orunconverted light emitted by the light-emitting die. The mountingsurface may have a reflectivity to visible light of approximately 95% toapproximately 98%. At least a portion of the outer contour of thephosphor element may have a surface texture for reducing total internalreflection. The light-emitting die may be a bare light-emitting diodedie. The light-emitting die may include or consist essentially of aGaN-based semiconductor material. The semiconductor material may includeIn. The light-emitting die may emit blue and/or ultraviolet light.

In yet another embodiment, aspects of the invention feature alight-emitting device that includes or consists essentially of alight-emitting die having (i) a top face and a bottom face opposite thetop face, the top and/or bottom face being configured for emission oflight therefrom, and (ii) a sidewall spanning the top and bottom faces,and at least partially surrounding the light-emitting die, a phosphorelement including or consisting essentially of (i) a binder and (ii)disposed within the binder, one or more wavelength-conversion materialsfor absorbing at least a portion of light emitted from thelight-emitting die and emitting converted light having a differentwavelength, converted light and unconverted light emitted by thelight-emitting die combining to form substantially white light. Thephosphor element includes or consists essentially of (i) a first regionhaving a sidewall substantially parallel to the sidewall of thelight-emitting die and (ii) disposed over the first region, a secondregion having a top surface defining a portion of an oblate ellipsoid.

Embodiments of the invention may include one or more of the following inany of a variety of different combinations. The second region may definea portion of an oblate ellipsoid described by the equation

${{z(r)} = \frac{r^{2}}{R\left( {1 + \sqrt{1 - {\left( {1 + K} \right)\left( {r^{2}/R^{2}} \right)}}} \right)}},$where z is a height of the second region above a top surface of thelight-emitting die, r is a radius of the oblate ellipsoid, R isapproximately 2.38, and K is approximately 6.0. The first region of thephosphor element may be discrete from and optically bonded to the secondregion of the phosphor element. The second region of the phosphorelement may be disposed over the top surface of the light-emitting die.A reflective surface may be disposed below the bottom surface of thelight-emitting die. The distance between the sidewall of the firstregion and the sidewall of the light-emitting die may be a value rangingfrom 0.2 mm to 20 mm. The distance between the sidewall of the firstregion and the sidewall of the light-emitting die may be a value rangingfrom 0.4 mm to 5 mm. Light emitted from the light-emitting die may havea Lambertian distribution. The converted light may have an isotropicdistribution. The divergence of color temperature of the substantiallywhite light emitted from the device may vary, over an angular range of0° to 85°, no more than 0.01 in terms of Δu′v′ deviation from aspatially weighted averaged chromaticity. The divergence of colortemperature of the substantially white light emitted from the device mayvary, over an angular range of 0° to 85°, no more than 0.005 in terms ofΔu′v′ deviation from a spatially weighted averaged chromaticity.

The one or more wavelength conversion materials may include or consistessentially of one or more phosphor particles. The phosphor particlesmay each include or consist essentially of garnet and a rare-earthelement. The light-emitting device may include, disposed beneath (i) atleast a portion of the light-emitting die and/or (ii) the phosphorelement, a mounting surface reflective to converted light and/orunconverted light emitted by the light-emitting die. The mountingsurface may have a reflectivity to visible light of approximately 95% toapproximately 98%. The top surface of the second region of the phosphorelement may have a surface texture for reducing total internalreflection. The light-emitting die may be a bare light-emitting diodedie. The light-emitting die may include or consist essentially of aGaN-based semiconductor material. The semiconductor material may includeIn. The light-emitting die may emit blue and/or ultraviolet light.

These and other objects, along with advantages and features of theinvention, will become more apparent through reference to the followingdescription, the accompanying drawings, and the claims. Furthermore, itis to be understood that the features of the various embodimentsdescribed herein are not mutually exclusive and can exist in variouscombinations and permutations. Reference throughout this specificationto “one example,” “an example,” “one embodiment.” or “an embodiment”means that a particular feature, structure, or characteristic describedin connection with the example is included in at least one example ofthe present technology. Thus, the occurrences of the phrases “in oneexample,” “in an example,” “one embodiment,” or “an embodiment” invarious places throughout this specification are not necessarily allreferring to the same example. Furthermore, the particular features,structures, routines, steps, or characteristics may be combined in anysuitable manner in one or more examples of the technology. The term“light” broadly connotes any wavelength or wavelength band in theelectromagnetic spectrum, including, without limitation, visible light,ultraviolet radiation, and infrared radiation. Similarly, photometricterms such as “illuminance,” “luminous flux,” and “luminous intensity”extend to and include their radiometric equivalents, such as“irradiance,” “radiant flux,” and “radiant intensity.” As used herein,the terms “substantially,” “approximately,” and “about” mean±10%, and insome embodiments, ±5%. The term “consists essentially of” meansexcluding other materials that contribute to function, unless otherwisedefined herein. Nonetheless, such other materials may be present,collectively or individually, in trace amounts.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the sameparts throughout the different views. Also, the drawings are notnecessarily to scale, emphasis instead generally being placed uponillustrating the principles of the invention. In the followingdescription, various embodiments of the present invention are describedwith reference to the following drawings, in which:

FIGS. 1A and 1B are plots of the simulated spectral radiant intensitydistribution of blue and yellow light, respectively, emitted from alight-emitting element and phosphor particles;

FIG. 2 is a schematic cross-section of a light-emitting device inaccordance with various embodiments of the invention, illustratingrefraction and total internal reflection of light;

FIGS. 3A, 3B, and 4A are schematic cross-sections of light-emittingdevices having shaped phosphor elements in accordance with variousembodiments of the invention;

FIGS. 4B-4D are, respectively, plots of the lighting-device emissionspectrum, phosphor-transmission spectrum, and phosphor-emission spectrumfor the lighting-devices of FIG. 4A;

FIG. 4E is a schematic cross-section of a light-emitting device having ashaped phosphor element in accordance with various embodiments of theinvention;

FIGS. 5A and 5B are plots of simulated chromaticity uniformity for alight-emitting device according to FIG. 4A;

FIG. 5C is a plot of simulated luminance flux for a light-emittingdevice according to FIG. 4A;

FIGS. 6A and 6B are plots of simulated chromaticity uniformity andluminance flux for a light-emitting device according to FIG. 4A;

FIGS. 6C and 6D are plots showing design guidelines for a light-emittingdevice according to FIG. 4A;

FIGS. 7A and 7B are plots of simulated chromaticity uniformity for alight-emitting device according to FIG. 4A;

FIG. 7C is a plot of simulated luminance flux for a light-emittingdevice according to FIG. 4A;

FIGS. 8A and 8B are plots of simulated chromaticity uniformity andluminance flux for a light-emitting device according to FIG. 4A;

FIGS. 8C and 8D are plots showing design guidelines a light-emittingdevice according to FIG. 4A;

FIG. 9 is a plot of chromaticity deviation for light-emitting devicesincorporating a hemispherical phosphor element or an engineered phosphorelement in accordance with various embodiments of the invention;

FIG. 10 is a plot of measured chromaticity deviation for light-emittingdevices incorporating an engineered phosphor element in accordance withvarious embodiments of the invention;

FIG. 11 is a schematic cross-section of a light-emitting deviceincorporating multiple phosphor regions in accordance with variousembodiments of the invention;

FIGS. 12A and 12B are plots of the simulated spectral radiant intensitydistribution of blue and yellow light, respectively, that exit thephosphor regions of FIG. 6;

FIG. 12C is a plot of chromaticity deviation for the light-emittingdevice of FIG. 6;

FIGS. 13A-13C are schematic cross-sections of portions of light-emittingdevices incorporating color equalization layers in accordance withvarious embodiments of the invention;

FIG. 14 is a schematic cross-section of a portion of a light-emittingdevice in accordance with various embodiments of the invention;

FIG. 15A-15E are schematic cross-sections of light-emitting devices inaccordance with various embodiments of the invention;

FIGS. 16A and 16B are schematic cross-sections of arrays of phosphorelements in accordance with various embodiments of the invention;

FIG. 16C is a schematic cross-section of a singulated phosphor elementin accordance with various embodiments of the invention; and

FIGS. 17A-17C are schematic cross-sections of pick-and-place toolsinteracting with light-emitting devices in accordance with variousembodiments of the invention.

DETAILED DESCRIPTION

Various embodiments of the present invention engineer (1) the angularintensity distribution of the light emitted from the LEE as it exits thesurrounding phosphor and (2) the angular intensity distribution of lightemitted from the phosphor to achieve a desired angular characteristic ofone or more optical parameters, for example to achieve a relativelyuniform color temperature with viewing angle. For example if the lightfrom the two sources, for example blue from an LEE and yellow from aphosphor, are engineered to have the same or substantially the sameangular intensity distribution, then the combination, when viewed orprojected externally to the phosphor, has the same or substantially thesame chromaticity as a function of angle. Thus, preferred embodiments ofthe invention control the angular intensity distribution of the lightemitted from the LEE and the light-conversion material as it exits thesurrounding phosphor. Various optical processes occur within thephosphor (for example absorption and scattering) and at the phosphor/airinterface (for example TIR and refraction) that modify the LEE angularintensity distribution from what it would be in the absence of anassociated phosphor, and embodiments of the invention account for suchprocesses, as will be detailed herein.

In one embodiment of the present invention, a combination of refractionfrom the top surface of the phosphor element and TIR from the interfacebetween the phosphor element and the surrounding air are used topreferentially redirect both (i) the light from the LEE that is notabsorbed by the phosphor particles and (ii) the light emitted by thephosphor particles in specific directions to achieve one or more desiredangularly dependent optical characteristics. In other words, thephosphor element is used not only to mechanically support the phosphoraround a portion of the LEE, but it is also used as a lens structurethat is optically coupled to the LEE and uses both TIR and refraction toredirect the pump light (e.g., blue light from the LEE) within the lensstructure such that the chromaticity of the emitted light (e.g., whitelight, being a combination of the blue pump light and the phosphoremissions) does not appreciably vary with the angle of emission. FIG. 2is a schematic of an exemplary system 200 of the present inventionfeaturing an LEE 130 and that utilizes both refraction (to produce, forexample, light 220) and TIR (to produce, for example, light 230) fromthe surface of a phosphor element 210.

FIGS. 3A and 3B depict two embodiments of the present invention, eachfeaturing a LEE 130 over which is disposed a phosphor element 140. InFIG. 3A, phosphor element 140 has a single-curve shape, i.e., a smoothcurve with no intermediate discontinuities. FIG. 3B shows anotherexample of phosphor element 140 having a two-curve shape, where the twoportions are identified as portions 330 and 340. In this case, portion340 is perpendicular to the bottom surface 315 of LEE 130; however, thisis not a limitation of the present invention, and in other embodimentsportion 340 may form an acute or obtuse angle with the bottom surface ofLEE 130. Various embodiments of this invention control the shape ofphosphor element 140, and in particular the shape of surfaces 330 and/or340. While FIGS. 3A and 3B show phosphor element 140 having one and twosurface curvatures respectively, this is not a limitation of the presentinvention, and in other embodiments phosphor element 140 may have morethan two such curvatures. As discussed herein, the shape and size ofphosphor element 140 is an important aspect of embodiments of thepresent invention.

Various factors, such as the dimensions of LEE die, mirrored activearea, phosphor matrix, phosphor particle concentration, and/or thediffuse and specular reflection properties of the LEE substrate, maysignificantly affect the TIR and refraction of both blue and yellow (forexample) light within the phosphor matrix. In general, numericalsimulation may be utilized to determine optimal shapes of the topsurface for given sets of design parameters. As detailed herein, TIR andrefraction may be used to redirect the light.

Example 1

FIG. 4A shows a schematic of one class of embodiments of the presentinvention, including or consisting essentially of LEE 130 partiallysurrounded by a phosphor element 420. In this example LEE 130 is a blueLEE, for example a blue LED, having an emission spectrum as shown inFIG. 4B. LEE 130 has a length of about 324 μm, a width of about 200 μm,and a height of about 134 μm. In these simulations the phosphor element420 is a hemispherical shape having a radius 410 of about 1 mm. Phosphorelement 420 has a refractive index of about 1.53 while LEE 130 has arefractive index of about 1.74. These simulations are optimized toproduce white light with a CCT of about 3500K and a color point on the1931 CIE chromaticity diagram of about 0.4 chromaticity x value and atabout 0.4 chromaticity y value using two phosphors, the emission spectraof which are shown in FIG. 4D. The combined mean-free-path of phosphorelement 420 is about 137 μm between simulation events (absorption,scattering, etc.); the phosphor transmission spectrum is shown in FIG.4C. Phosphor element 420 is defined as a function of a hemisphericalprofile with a radius 410. FIG. 4A also shows additional optionalfeatures of phosphor element 420, including a centroid z-offset 430, acylindrical cut-off having diameter 440 that in some embodiments resultsin a second portion of the shape of phosphor 140, for example portion340 shown in FIG. 3B, and a flat-top z-offset 450 that results in a flattop 460 having a flat top radius (not identified in FIG. 4A). Any one orall of these features may be combined in phosphor element 420. Thestructure of FIG. 4A may also be described as a hemispherical cap, thatis a portion of a hemisphere cut off by a plane above the base of thehemisphere, as shown in FIG. 4E (for reference a hemispherical cap witha centroid z-offset of zero (0) is a hemisphere). FIG. 4E showshemisphere 470 having a radius 410 and hemispherical cap 475 with LEE130 sitting on the plane forming the base 490 of hemispherical cap 475.The hemispherical cap height is identified as 480, the centroid z-offsetis identified as 430, and the hemispherical cap radius is identified as411. The structure in FIG. 4E does not show optional flat top 460 or thecylindrical cut-off shown in FIG. 4A.

FIGS. 5A and 5B show the chromaticity uniformity while FIG. 5C shows theluminous flux for the structure of FIG. 4A, as a function of centroidz-offset 430 and flat top z-offset 450. FIGS. 5A and 5B show the samedata but from different orientations. FIG. 5B also shows a contour plotof chromaticity uniformity. In FIGS. 5A-5C both centroid z-offset andflat top z-offset values are normalized to the hemisphere radius 410.Chromaticity uniformity (sum of Δ u′ v′) is measured as the sum of thedeviation of u′v′ from the spatially averaged chromaticity coordinateover 0° to 90° polar angles as defined in IES LM-79-08, “Electrical andPhotometric Measurements of Solid-State Lighting Products,” IlluminatingEngineering Society, January 2008 (where 0° is perpendicular to theemitting face of LEE 410), the entire disclosure of which isincorporated by reference herein.

As may be seen in FIGS. 5A and 5B, there is an unexpected minimum in theangular chromaticity uniformity for centroid z-offset values in therange of about 0.3 to about 0.7. Thus, instead of positioning LEE 130 atthe base or equator of the hemisphere, as is conventionally done, asignificant improvement in chromaticity uniformity may be realized bypositioning LEE 130 above the base or equator of the hemisphere. As maybe seen from FIGS. 5A and 5B, the uniformity relative to an LEE 130 atthe base or equator of the hemisphere may improve by over a factor ofthree. FIG. 5C shows that the luminance flux increases essentiallymonotonically with an increase in the centroid z-offset. As may be seenfrom FIGS. 5A-5C, the flat top z-offset has a relatively smaller impacton chromaticity uniformity and luminance flux. However, as will bediscussed herein, there may be other reasons for incorporating a flattop, and FIGS. 5A-5C show that incorporation of a flat top hasrelatively little impact on the chromaticity uniformity and luminanceflux.

FIGS. 6A and 6B show plots of chromaticity uniformity and luminance fluxas a function of centroid z-offset at two flat top z-offset values,about 0.02 and about 0.12 respectively. In FIGS. 6A and 6B, bothcentroid z-offset and flat top z-offset values are normalized to radius410. As may be seen there is a clear minimum in chromaticity uniformity(or chromaticity deviation) in the range of centroid z-offset from about0.3 to about 0.7. As the flat-top z-offset value increases, the amountof centroid z-offset required to minimize the chromaticity variationdecreases. For a flat top z-offset of about 0.02 (almost a hemisphere),the optimal centroid z-offset is in the range of about 0.57 to about0.7, or in the range of about 0.6 to about 0.675. For a larger flat topz-offset of about 0.12, the optimal centroid z-offset is in the range ofabout 0.375 to about 0.5, or in the range of about 0.4 to about 0.475.

As may be seen from FIGS. 6A and 6B, the luminance flux increasessubstantially monotonically with increasing centroid z-offset. In someembodiments, luminance flux intensity may be relatively more importantthan angular chromaticity uniformity, and in these embodiments a largercentroid z-offset value may be chosen to increase luminance fluxintensity while still maintaining relatively high angular chromaticityuniformity. For example, for the embodiment where the flat top z-offsetis about 0.02, the centroid z-offset may be in the range of about 0.65to about 0.7. For the embodiment where the flat-top z-offset is about0.12, the centroid z-offset may be in the range of about 0.45 to about0.5. As may be seen, there is a relatively substantial overlap betweenthe values of centroid z-offset to achieve minimum angular chromaticityvariation and to achieve high luminous flux.

FIG. 6C shows a plot of centroid z-offset (normalized to hemisphereradius 410) as a function of flat top z-offset (normalized to hemisphereradius 410) to achieve minimum angular chromaticity variation. In someembodiments, FIG. 6C may be used as a design guide to achieve minimumangular chromaticity variation. First the desired flat top z-offset isdetermined, then FIG. 6C is used to determine the optimal centroidz-offset to achieve minimum angular chromaticity variation. A linefitted to the data gives a relationship of H=−1.90×F+0.67, where F isthe flat top z-offset and H is the centroid z-offset. As may be seenfrom FIGS. 5A and 5B, there is relatively little variation in angularchromaticity non-uniformity as a function of flat top z-offset, when apreferred value for centroid z-offset is chosen.

FIG. 6D shows the same data as FIG. 6C, but with the addition ofluminance flux. The luminance flux data shown in FIG. 6C is the value atthe minimum angular chromaticity non-uniformity for each value of flattop z-offset. As may be seen from FIG. 6D, smaller flat top z-offsetvalues give a relatively larger luminance flux, but the total variationin luminance flux in FIG. 6D is relatively small, on the order of about10%.

FIGS. 7A-7C show angular chromaticity uniformity and luminance flux as afunction of centroid z-offset and hemisphere radius, respectively. Inthis example, the flat top z-offset is zero and the hemisphere radius isvaried from 0.4 to 1.6 mm. The size of LEE 130 and other simulationparameters are the same as for FIGS. 5A-5C and FIGS. 6A-6C. As may beseen from FIGS. 7A and 7B, varying the hemisphere radius does not changethe unexpected result that the angular chromaticity uniformity isminimized with a relatively large centroid z-offset. There is a slightimprovement in angular chromaticity uniformity with increasinghemisphere radius, but as will be seen in connection with FIGS. 8A and8B, this is relatively small. Similar to the plot of FIG. 6C, the plotin FIG. 7C shows that the luminance flux increases with increasingcentroid z-offset and also increases with increasing hemisphere radius.

FIGS. 8A and 8B show plots of chromaticity uniformity and luminance fluxas a function of centroid z-offset at two hemisphere radius values,about 0.90 mm and about 1.5 mm respectively. As may be seen there is aminimum in angular chromaticity uniformity for higher values. Incomparison to FIGS. 6A and 6B, there is a relatively strongercorrelation between the centroid z-offset position for minimum angularchromaticity uniformity and hemisphere radius, than for centroidz-offset position and flat top z-offset. As the hemisphere radiusincreases, the required value of centroid z-offset to minimizechromaticity variation increases. For a hemisphere radius of about 0.90mm, the optimal centroid z-offset is in the range of about 0.5 mm toabout 0.6 mm, or in the range of about 0.525 mm to about 0.575 mm. Ifthese values are normalized to the hemisphere radius, then the rangesare about 0.55 to about 0.67 and about 0.58 to about 0.64. For ahemisphere radius of about 1.5 mm, the optimal centroid z-offset is inthe range of about 0.8 mm to about 1.15 mm, or in the range of about 0.9mm to about 1.1 mm. If these values are normalized to the hemisphereradius, then the ranges are about 0.53 to about 0.77 and about 0.60 toabout 0.73.

As may be seen from FIGS. 8A and 8B, the luminance flux increasessubstantially monotonically with increasing centroid z-offset. In someembodiments, luminance flux intensity may be relatively more importantthan angular chromaticity uniformity, and in these embodiments a largercentroid z-offset value may be chosen to increase luminance fluxintensity while still maintaining relatively high angular chromaticityuniformity. For example, for an embodiment in which the hemisphereradius is about 0.9 mm, the centroid z-offset may be in the range ofabout 0.5 to about 0.6. As may be seen from FIG. 8A, the region ofcentroid z-offset to achieve high luminance flux and reduced angularchromaticity exhibit substantial overlap. For the embodiment where theflat-top z-offset is about 0.90, the centroid z-offset may be in therange of about 0.5 to about 0.6.

FIG. 8C shows a plot of centroid z-offset as a function of hemisphereradius to achieve minimum angular chromaticity variation. In someembodiments, FIG. 8C may be used as a design guide to achieve minimumangular chromaticity variation. First, the desired hemisphere radius isdetermined, then FIG. 8C may be used to determine the optimal centroidz-offset to achieve minimum angular chromaticity variation. A linefitted to the data gives a relationship of H=−1.41×R−0.80, where R isthe hemisphere radius and H is the centroid z-offset.

FIG. 8D shows the same data as FIG. 8C, but with the addition ofluminance flux. The luminance flux data shown in FIG. 8C is the value atthe minimum angular chromaticity non-uniformity for each value ofhemisphere radius. As may be seen from FIG. 8D, smaller hemisphereradius values give a relatively larger luminance flux, but the totalvariation in luminance flux in FIG. 8D is relatively small, on the orderof about 10%.

The structural parameters associated with the minimum angularchromaticity variation region from FIG. 5B are a radius in the range ofabout 0.9 mm to about 1.1 mm and a centroid z-offset of about 0.5 mm toabout 0.7 mm, and more particularly a radius of about 0.93 mm to about 1mm and a centroid z-offset of about 0.55 mm to about 0.65 mm. In oneembodiment, the hemisphere has a radius in the range of about 0.6 mm toabout 1.2 mm and a centroid z-offset value (normalized to the hemisphereradius) in the range of about 0.5 to about 0.8. In one embodiment, thehemisphere has a radius in the range of about 0.8 mm to 1.2 mm and acentroid z-offset value (normalized to the hemisphere radius) in therange of about 0.4 to about 0.8 and a flat top z-offset (normalized tohemisphere radius) in the range of about 0.02 to 0.15. In oneembodiment, the hemispherical cap radius is about 0.6 mm to about 1.0mm, height 480 is in the range of about 0.15 mm to about 0.5 mm, and theflat top radius is in the range of about 0.15 to about 0.45 mm. In oneembodiment, the hemispherical cap radius is about 0.6 mm to about 1.0mm, the centroid offset is about 0.5 mm to about 0.6 mm, and the flattop z-offset is about 0.02 mm to about 0.08 mm. In one embodiment, thehemispherical cap radius is about 0.96 mm, the centroid offset is about0.54 mm, and the flat top z-offset is about 0.05 mm. In someembodiments, the hemispherical cap has a base radius of about 0.5 mm toabout 1.0 mm; however, this is not a limitation of the presentinvention, and in other embodiments the base of hemispherical cap mayhave a larger or smaller base radius. In some embodiments, the diameterof the flat top is in the range of about 50 μm to about 1000 μm;however, this is not a limitation of the present invention, and in otherembodiments the flat top may have a larger or smaller diameter. In someembodiments, the diameter of the flat top is in the range of about 200μm to about 800 μm. In some embodiments, the centroid z-offset is in therange of about 25 μm to about 300 μm; however, this is not a limitationof the present invention, and in other embodiments the centroid z-offsetmay be larger or smaller. In some embodiments, the centroid z-offset isin the range of about 50 μm to about 150 μm. In some embodiments, thehemisphere radius is in the range of about 100 μm to about 20 mm;however, this is not a limitation of the present invention, and in otherembodiments the hemisphere radius may be larger or smaller.

While the discussion with respect to the structures shown herein haveidentified a hemisphere radius in the range of about 0.4 mm to about 1.6mm, this is not a limitation of the present invention, and in otherembodiments hemisphere radius may be smaller or larger. For example, insome embodiments the hemisphere radius may be 2 mm in diameter or 5 mmin diameter or larger. In some embodiments, the hemisphere radius may besmaller than 0.4 mm, for example 0.2 mm or smaller.

Example 2

Example 2 is one embodiment of the approach discussed above. FIG. 9shows the deviation in chromaticity Δu′v′ from the spatially averagedchromaticity as a function of angle for an engineered shape of aphosphor element similar to that shown in FIG. 3B. The deviation inchromaticity over a variety of angles was simulated using Monte Carloray-tracing techniques with ten million light rays. In this case, theshape of phosphor element 140 is defined as a function of ahemispherical profile with a radius of about 800 μm, centroid depthoffset of about 410 μm (measured from the center of the bottom surface315 of the LEE 130), circular flat-top of about 500 μm in diameter, anda cylindrical cut-off of about 1200 μm diameter. The characteristics ofphosphor 140 and LEE 130 are the same as in Example 1. FIG. 9 also showsthe deviation in chromaticity for a hemisphere with a radius of about800 μm and centroid depth offset of about 0 μm, showing poorerperformance (i.e., greater deviation in chromaticity) of the hemispherecompared to the engineered shape.

The discussion above has focused on hemispherical-shaped phosphorelements 130; however, this is not a limitation of the presentinvention, and in other embodiments phosphor element 130 may be definedby other shapes. For example, phosphor element 130 may have a topsurface that defines a portion of an oblate ellipsoid.

Example 3

FIG. 10 shows the measured deviation in chromaticity Δu′v′ from thespatially average chromaticity as a function of angle for an engineeredshape of a phosphor element similar to that shown in FIG. 3B. In thiscase the shape of portion 330 of the phosphor element 140 is defined asa function corresponding to an oblate ellipsoid profile described by theequation:

${z(r)} = \frac{r^{2}}{R\left( {1 + \sqrt{1 - {\left( {1 + K} \right)\left( {r^{2}/R^{2}} \right)}}} \right)}$where r is the horizontal distance measured radially from the centralaxis, z is the distance (at r) to the surface, measured vertically withrespect to the horizontal plane that touches the surface at r=0, R=2.38,and K=6.0. The phosphor element 140 has a refractive index of about 1.53with a transmission spectrum shown in FIG. 4B. The phosphor emissionspectrums targets a 3500 K CCT at about 0.4 chromaticity x value and atabout 0.4 chromaticity y value, the phosphor has the samecharacteristics as discussed in Example 1 and LEE 130 has the samedimensions and characteristics as in Example 1. As may be seen from FIG.10, the measured deviation in chromaticity Δu′v′ from the spatiallyaverage chromaticity as a function of angle is significantly lower thanthat for the hemisphere (shown in FIG. 9).

An oblate ellipsoid is mathematically defined by the quadratic equation:

${\frac{x^{2}}{a^{2}} + \frac{y^{2}}{b^{2}} + \frac{z^{2}}{c^{2}}} = {{1\mspace{14mu}{where}\mspace{14mu} a} = b}$x² /a ² +y ² /b ² +z ² /c ²=1

where a=b

and has a shape intermediate between a hemisphere and a paraboloid. Aparticular advantage of an ellipsoid over a more complicated shape (asdescribed for example by a higher order cubic or quatric equation) isthat it has a smoother shape. This smoothness is preferred order toavoid discontinuities in the spatial distribution that are visible ascaustics. (The rings of light visible in the projected beams from MR16halogen lamps are a good example.)

As discussed above, preferred embodiments of the invention position theLEE away from the center of an oblate ellipsoid (such as, for example,the center of a hemisphere). Positioning the LEE at the center generallymaximizes the symmetry of the LEE such that all light paths (includingscattering and absorption/emission) are substantially the same, thuspreventing the modification of the light paths to achieve improvedangular uniformity. Preferred embodiments also position the LEE awayfrom the surface of the oblate ellipsoid. When the LEE is at thesurface, there is typically an insufficient mean free path between theLEE and the phosphor boundary to adequately balance the ratio of bluelight and phosphor emissions to generate white light. Variousembodiments of the invention feature a rectangular LEE whose length isgreater than approximately twice its width and a phosphor element havingthe shape of a tri-axial ellipsoid where c>b>a.

In another embodiment, LEE 130 may be embedded or partially embedded ina series of multiple phosphor elements. For example, in one embodiment,a phosphor element 1110 and a phosphor element 1120 may be formed overor partially formed over LEE 130, as shown in FIG. 11. In oneembodiment, phosphor element 1110 is different from phosphor element1120. The differences between phosphor element 1110 and 1120 may includea different binder material, a different type of phosphor particle(1170, 1180) or particles, a different index of refraction, differentconcentrations of phosphor particles, or the like.

In some embodiments, a reflective surface, for example surfaces 1160and/or 1165, may be formed below all or a portion of LEE 130 and/orphosphors 1110, 1120. In some embodiments, surface 1160 may include orconsist essentially of a diffuse or specular reflector. In oneembodiment, surface 1160 may include or consist essentially of a metal,for example aluminum, copper, silver, gold or the like. In someembodiments, surface 1160 may include or consist essentially of adiffuse reflector, such as a white surface, for example a white ink, ormaterial such as multicellular polyethylene terephthalate (MCPET) orpolyester. In some embodiments, reflective surface 1165, as shown inFIG. 11, may be incorporated into LEE 130.

More generally, the two or more phosphor element binders may havedifferent refractive indices. If, for example, a first phosphor elementbinder 1140 has a lower refractive index than a second phosphor elementbinder 1130, TIR may occur at their boundary, thereby increasing theamount of blue light redirected to the sides of the first phosphorelement. Alternatively, if the two or more optical elements are adheredwith a glue or adhesive, the optical glue material may have a higherrefractive index, thereby increasing the TIR at the boundary. Inaddition, the boundary between the first and second phosphor elementsmay include a dichroic mirror that is transparent to blue light butwhich reflects longer wavelengths.

Example 4

FIG. 11 depicts an LEE die 130 that has a length of about 325 μm, awidth of about 200 um and a height of about 135 μm, as well as a mirroror reflective surface 1165 having dimensions of about 205 μm long and150 μm wide. In this example, mounting surface 1160 (on which the LEEdie 130 is mounted) has a reflectivity of about 95% to about 98% overthe visible wavelength range, and may include or consist essentially ofa material such as MCPET. Phosphor element 1110, disposed around the LEEdie 130, includes binder 1130 into which are dispersed phosphorparticles 1170. In this example, binder 1130 includes or consistsessentially of a silicone and has a refractive index of about 1.57.Phosphor element 1110 is about 1200 μm long, about 1200 μm wide andabout 165 μm tall.

Second phosphor element 1120, which is disposed over the top surface ofthe LEE die 130, includes or consists essentially of, in this example, asilicone binder 1140 with a refractive index of about 1.57 andcontaining phosphor particles 1180 with a density that is about 33%greater than that of the phosphor element 1110. The phosphor element1120 may be optically bonded to the top surface of phosphor element1110. Phosphor element 1120 is about 1200 μm long and about 1200 μm widewith a maximum height of about 435 μm.

A curved upper surface 1190 of the phosphor element 1120 has an oblateellipsoid profile described by the equation:

${z(r)} = \frac{r^{2}}{R\left( {1 + \sqrt{1 - {\left( {1 + K} \right)\left( {r^{2}/R^{2}} \right)}}} \right)}$where r is the radius, z is the height (measured from the center of thetop surface), R=2.38 and K=6.0. The profile was determined by iterativenumerical simulations to provide an optimal distribution of blue andyellow light that minimizes chromaticity variations with respect to theviewing angle θ.

FIGS. 12A and 12B show the simulated spectral radiant intensitydistribution of the blue and yellow light, respectively, that exit boththe first and second phosphor matrices. As shown, the radiant intensitydistributions of blue and yellow light in FIGS. 12A and 12B are quitesimilar to each other, indicating that this system has relativelyuniform chromaticity over a large range of viewing angles. FIG. 12Cshows the deviation in chromaticity Δu′v′ from the spatially averagechromaticity as a function of angle for Example 4.

In another embodiment of the present invention, a color equalizationlayer (CEL) is interposed between the LEE and the phosphor. The CELrefers to a structure located between the LEE and the phosphor thatincludes or consists essentially of a material of lower absorptioncoefficient than the phosphor. The shape or absorption properties of theCEL are designed to provide angular modulation of the absorption of theLEE light, in such a way that the angular distribution of the LEE lightintensity after passing through the phosphor is more closely matched tothe angular distribution of the converted light. The CEL and thesurrounding phosphor are typically index matched or substantially indexmatched to eliminate or substantially eliminate TIR at their interface.In one embodiment, the CEL may include or consist essentially of asubstantially optically transparent material (the binder) or a materialhaving a lower absorption efficiency than the phosphor element. In oneembodiment, the CEL may also be a phosphor material (e.g., a binderhaving therewithin a plurality of phosphor or otherwavelength-conversion particles) and have a lower absorption efficiencythan that of the outer phosphor element. Preferred embodiments of theinvention provide an interface adjacent to two or more index-matched ornearly index-matched regions, which may be shaped as required tooptimize color uniformity while minimizing TIR or other effects that mayimpact extraction efficiency or other performance characteristics of thephosphor-converted package.

FIGS. 13A-13C depict exemplary illumination systems 1300, 1301, and1302, respectively, in accordance with embodiments of the presentinvention, although alternative systems with similar functionality arealso within the scope of the present invention. As may be seen fromFIGS. 13A-13C, a CEL 1341 is disposed between LEE 130 and phosphor 140.In various embodiments, the optical properties of CEL 1341 may behomogeneous and the shape of CEL may be varied to provide the desiredmodification of the angular intensity distribution of light emitted bythe LEE, as shown in FIGS. 13B and 13C. As may be seen schematically inFIGS. 13B and 13C, the exterior shape of phosphor 140 may be varied aswell, and the shape of CEL 1341 is preferably modified accordingly.Procedures for determining the shape of CEL 1341 are provided herein. Inother embodiments, CEL 1341 may have a relatively arbitrary shape, forexample conformably similar to LEE 130 and/or phosphor 140 and haveinhomogeneous optical properties, for example absorption or scattering,to provide the desired modification of the angular intensitydistribution of light emitted by the LEE, as shown in FIG. 13A.

The inventors have found that a key aspect of the shapes of the CEL 1341is that the thickness of the CEL measured vertically from the planeparallel to and intersecting the bottom surface of LEE 130, has amaximum thickness at a position intermediate between the center of LEE130 and the outer edge of the CEL 1341 or phosphor 140. In someembodiments, the thickness of the CEL 1341 is zero or substantially zeroat the center of LEE 130 (as shown in FIGS. 13B and 13C). Thus, theshape of CEL 1341 may be described as optionally starting on the surfaceof LEE 130 at the center of LEE 130, increasing monotonically towardsthe edge of LEE 130, reaching a maximum thickness after passing the edgeof LEE 130, and then decreasing monotonically until reaching the planeparallel to the bottom surface of LEE 130. Note that this description isfor one-half of the rotationally symmetric shape, starting at the centerof the structure. The full three-dimensional shapes of CEL 1341 andphosphor 140 are realized by rotating the cross-section about they-axis.

Example 5

Example 5 is based on the structure shown in FIG. 13B. Phosphor 140 hasa cylindrical shape with the axis of the cylinder aligned with thecenter of LEE 130. Phosphor 140 has a height of about 0.5 mm and adiameter of about 1 mm. In this embodiment, CEL 1341 is opticallytransparent and is substantially the same as the binder in phosphor 140.LEE 130 is a cylindrical disk having a height of about 0.1 mm and aradius of about 0.2 mm. The shape of the interface between CEL 1341 andphosphor 140 is engineered to minimize the difference in (1) the angularintensity distribution of the light emitted from LEE 130 as it exitsphosphor 140 and (2) the angular intensity distribution ofwavelength-converted light emitted from phosphor 140 such that they arethe same or substantially the same.

Example 6

Example 6 is based on the structure shown in FIG. 13C. Phosphor 140 hasa hemispherical shape with the axis of the hemisphere aligned with thecenter of LEE 130. The hemispherical shape may result in increased lightoutput power because of reduced TIR at the interface between phosphor140 and air. Phosphor 140 has a radius of about 1 mm. In thisembodiment, CEL 1341 is optically transparent and is substantially thesame as the binder in phosphor 140. LEE 130 is a cylindrical disk havinga height of about 0.1 mm and a radius of about 0.2 mm. The shape of theinterface between CEL 1341 and phosphor 140 is engineered to minimizethe difference in (1) the angular intensity distribution of the lightemitted from LEE 130 as it exits phosphor 140 and (2) the angularintensity distribution of wavelength-converted light emitted fromphosphor 140 such that they are the same or substantially the same.

Using these principles, the shape of CEL 1341 may be determined withoutundue experimentation by one skilled in the art by first determining theradiant flux distribution pattern of LEE 130 as a function of angle,simulating the entire structure to determine the angular intensitydistribution of blue light emitted from the outer surface of phosphor140 and then adjusting the boundary between CEL 1341 and phosphor 140such that the angular intensity distribution of blue light emittedthrough the outer surface of the phosphor 140 substantially matches theangular distribution of the phosphor-converted light emitted fromphosphor 140.

In some embodiments, the interior and/or exposed surfaces of thephosphor and/or binder may be smooth or textured, depending on thedesired intensity distribution. Additionally, these surfaces may beintentionally roughened or textured, for example, to further control thedesired intensity distribution. Such modification of the varioussurfaces may also be used to increase the light-extraction efficiency byreducing TIR. FIG. 14 shows an example of one embodiment of a structurein which the outer surface of phosphor 140 is roughened or textured,identified as surface 1410 in FIG. 14. While FIG. 14 shows all of thecurved surface of phosphor 140 as being roughened or textured this isnot a limitation of the present invention, and in other embodiments onlya portion of phosphor 140 may be textured or roughened. Texturing orroughening of phosphor 140 may be accomplished by a variety of means,for example using ablation or etching, or phosphor 140 may be formedwith a roughened or textured surface, for example by molding or casting.In some embodiments, the texturing or roughening may be random, while inother embodiments the texturing or roughening may be periodic. In someembodiments, the texturing or roughening may have a feature size in therange of about 0.1 μm to about 5 μm; however, the size and extent anddensity of texturing or roughening is not a limitation of the presentinvention.

In some embodiments, the structures described herein, including orconsisting essentially of an LEE and a phosphor element, hereinidentified as an LEE/phosphor element, may be incorporated into packagesto produce packaged LEEs with improved angular chromaticity uniformity.For example, FIGS. 15A-15E show examples of embodiments of LEE 130 andphosphor 140 incorporated into packaged devices.

For example each LEE/phosphor element may be mounted on a base orsubstrate, as identified as 1565 and 1592 in FIGS. 15A and 15Brespectively; however, this is not a limitation of the presentinvention, and in other embodiments LEE/phosphor elements within thescope of this invention may be unmounted or unpackaged, for example asshown in FIG. 15C. FIG. 15C shows an example of a structure identifiedas a white die 1502 that includes or consists essentially of an LEE 130and a phosphor 140. White die 1502 is described in U.S. patentapplication Ser. No. 13/748,864, filed on Jan. 24, 2013, the entiredisclosure of which is herein incorporated by reference.

In some embodiments of the present invention, contacts 1580, 1585 of LEE130 may be electrically coupled and/or attached to conductive traces orconductive elements, as identified as 1560 or 1590 in FIGS. 15A and 15Brespectively. Contacts 1580, 1585 of LEE 130 may be electrically coupledand/or attached to conductive traces 1560 or 1590 using a variety ofmeans; the method of electrical coupling and/or attachment is not alimitation of the present invention. In some embodiments, contacts 1580,1585 of LEE 130 may be electrically coupled and/or attached toconductive traces 1560 or 1590 using a conductive adhesive, a conductivepaste, an anisotropic conductive film, or another type of anisotropicconductive adhesive (ACA), as shown in FIG. 15A. In some embodiments,contacts 1580, 1585 of LEE 130 may be electrically coupled and/orattached to conductive traces 1560 or 1590 using wire bonds 5191 asshown in FIG. 15B. In some embodiments, LEE 130 may be attached toconductive traces 1560 or 1590 using a conductive adhesive and/or anon-conductive adhesive. In some embodiments, contacts 1580, 1585 of LEE130 may be electrically coupled and/or attached to conductive traces1560 or 1590 using a solder process, eutectic solder process, wavesolder process, or a solder reflow process. In some embodiments, LEE 130may be electrically coupled and/or attached to conductive traces 1560 or1590 in a flip-chip orientation, for example as shown in FIGS. 15A and15D. The method of electrical coupling and/or attachment of contacts1580, 1585 to conductive traces 1560 or 1590 is not a limitation of thepresent invention.

The structures shown in FIGS. 15A-15C include one LEE 130; however, thisis not a limitation of the present invention, and in other embodimentsthe structure may include multiple LEEs 130, as shown in FIG. 15D. FIG.15D shows a structure 1503 that includes a substrate 1592 over which hasbeen formed conductive elements 1560 and to which contacts 1580 and 1585(not shown for clarity) of LEEs 130 have been electrically coupled. Thestructure shown in FIG. 15D may also be referred to as a chip-on-boardstructure. Contacts 1580 and 1585 may be attached using a variety ofmeans, for example wire bonding, solder, adhesive, and the like.Exemplary structure 1503 includes four LEEs 130; however, this is not alimitation of the present invention, and in other embodiments structure1503 may include any number of LEEs 130, e.g., 10 or 20. Structure 1503also includes package contacts 1591, 1593 to which conductive elements1560 are electrically coupled and which are typically electricallyconnected to an external power source. FIG. 15E shows a structureincluding more than one LEE/phosphor element structure, featuring a lineor array of LEE/phosphor element structures formed over a substrate1594. In some embodiments, phosphor element 140 may have a radius of atleast 2 mm, or at least 5 mm. In some embodiments, for example wherephosphor element 140 encompasses more than one LEE 130 (for example asshown in FIG. 15D), phosphor element 140 may have a relatively largerradius, for example over 5 mm or over 10 mm or over 30 mm.

Substrates 1565 and 1592 may be composed of a wide range of materials.In some embodiments, substrates 1565 and 1592 may have relatively lowthermal conductivities. In some embodiments, substrates 1565 and 1592may have relatively high thermal conductivities. In some embodiments,substrates 1565 and 1592 may be flexible, while in others they may besubstantially rigid. Substrate 1565 may include or consist essentiallyof a semicrystalline or amorphous material, e.g., polyethylenenaphthalate (PEN), polyethylene terephthalate (PET), polycarbonate,polyethersulfone, polyester, polyimide, polyethylene, and/or paper.Substrate 1565 may include or consist essentially of multiple layers,e.g., a deformable layer over a rigid layer, for example, asemicrystalline or amorphous material, e.g., PEN, PET, polycarbonate,polyethersulfone, polyester, polyimide, polyethylene, and/or paperformed over a rigid substrate comprising, e.g., acrylic, aluminum,steel, and the like. Depending upon the desired application for whichembodiments of the invention are utilized, substrate 1565 may besubstantially optically transparent, translucent, or opaque. Forexample, substrate 1565 may exhibit a transmittance or a reflectivitygreater than 70% for optical wavelengths ranging between approximately400 nm and approximately 600 nm. In some embodiments, substrate 1565 mayexhibit a transmittance or a reflectivity of greater than 70% for one ormore wavelengths emitted by LEE 130 and or phosphor 140. Substrate 1565may also be substantially insulating, and may have an electricalresistivity greater than approximately 100 ohm-cm, greater thanapproximately 1×10⁶ ohm-cm, or even greater than approximately 1×10¹⁰ohm-cm. In some embodiments, substrates 1565 or 1592 may include orconsist essentially of materials such as fiberglass, FR4, metal, ceramicmaterials such as silicon carbide, aluminum nitride, aluminum oxide,combinations of these materials, and the like. In some embodiments,substrate 1565 or 1592 may include or consist essentially of a metal,for example a metal leadframe. In some embodiments, substrate 1565 or1592 may include or consist essentially of a metal-core printed circuitboard. The material and form of substrates 1565 or 1592 is not alimitation of the present invention.

Conductive elements 1560 and 1590 may be formed via conventionaldeposition, photolithography, and etching processes, plating processes,lamination, lamination and patterning, evaporation sputtering, chemicalvapor deposition or the like, or they may be formed using a variety ofprinting processes. For example, conductive elements 1560 and 1590 maybe formed via screen printing, flexographic printing, ink-jet printing,and/or gravure printing. Conductive elements 1560 and 1590 may includeor consist essentially of a conductive ink, which may include one ormore elements such as silver, gold, aluminum, chromium, copper, and/orcarbon. Conductive elements 1560 and 1590 may include or consistessentially of a conductive material, which may include one or moreelements such as silver, gold, aluminum, chromium, copper, and/orcarbon. Conductive elements 1560 and 1590 may have a thickness in therange of about 50 nm to about 500 μm; however, the thickness ofconductive elements 1560 and 1590 is not a limitation of the presentinvention. In some embodiments, all or a portion of conductive elements1560 and 1590 may be covered or encapsulated. In some embodiments, alayer of material, for example insulating material, may be formed overall or a portion of conductive elements 1560 and 1590. Such a materialmay include or consist essentially of, for example, a sheet of materialsuch as that used for substrate 1565, a printed layer, for example usingscreen, ink jet, stencil or other printing techniques, a laminatedlayer, or the like. Such a layer may include or consist essentially of,for example, an ink, a plastic and oxide or the like. The coveringmaterial and/or the method by which it is applied is not a limitation ofthe present invention.

In one embodiment, conductive traces 1560 may be formed so as to have agap between adjacent conductive traces 1560, and LEEs 130 areelectrically coupled to conductive traces 1560 using conductiveadhesive, e.g., an isotropically conductive adhesive and/or an ACA 1561,for example as shown in FIG. 15A. ACAs may be utilized with or withoutstud bumps and embodiments of the present invention are not limited bythe particular mode of operation of the ACA. For example, the ACA mayutilize a magnetic field rather than pressure (e.g., the ZTACH ACAavailable from SunRay Scientific of Mt. Laurel, N.J., for which amagnetic field is applied during curing in order to align magneticconductive particles to form electrically conductive “columns” in thedesired conduction direction). Furthermore, various embodiments utilizeone or more other electrically conductive adhesives, e.g., isotropicallyconductive adhesives, non-conductive adhesives, in addition to orinstead of one or more ACAs.

In some embodiments, the shape of phosphor element 140 is formed bycasting or molding. In some embodiments, multiple phosphor elements maybe formed separately. In some embodiments, multiple phosphor elementsmay be formed simultaneously. In some embodiments where multiplephosphor elements are formed simultaneously, each element 140 may beseparated from adjacent shapes by a web 1610, for example as shown inFIG. 16A. In some embodiments, the elements may be formed in a mergedfashion, for example as shown in FIG. 16B, where adjacent phosphorelements 140 are merged at an interface 1620. In some embodiments, thestructure in FIG. 16B permits the manufacture of a larger number ofphosphor elements 140 in a fixed area, as compared to the structure ofFIG. 16A. In a subsequent manufacturing step, phosphor elements 140shown in FIG. 16A or 16B may be separated or singulated. For example,the structure of FIG. 16B may be singulated at a cut line 1630. Aftersingulation the structure may look like the example shown in FIG. 16C,having a cylindrical cutoff 440, as described in reference to FIG. 4A,and a removed portion having extent 1640, as shown in FIG. 16C. In someembodiments, the ratio of dimension 440 to the hemisphere diameter(which is two times the hemisphere radius) is in the range of about 0.95to about 0.75. In some embodiments the cut-off portion is in the rangeof about 50 μm to about 500 μm.

During the manufacture of structures described herein, for examplestructures shown in FIGS. 15A-15E, it may be necessary to move or pickup structures such as those shown in FIGS. 3A and 3B. In someembodiments, pick-and-place equipment may be used. Pick-and-place toolsare conventionally used to pick up semiconductor dies. These may operateat very high speeds, for example at least 5000 units per hour or atleast 10,000 units per hour. The pick-and-place equipment may have avacuum tip that is applied to the flat top of each semiconductor die.When vacuum is applied to the vacuum tip, the semiconductor die istemporarily attached to the tip, and thus may be moved from one locationto the next. A schematic of this is shown in FIG. 17A, showing vacuumtool 1710 and semiconductor die 1720. However, the curved top surface ofphosphor element 140 may render it difficult to achieve a good sealbetween vacuum tool 1710 and phosphor element 140 as shown in FIG. 17B.In some embodiments, a flat top may be formed on the top of phosphorelement 140, as shown in FIG. 17C, to provide a flat surface for sealingof vacuum tool 1710 to phosphor element 140. In some embodiments, theflat top may have a diameter in the range of about 50 μm to about 1000μm; however, this is not a limitation of the present invention, and inother embodiments the flat top may be larger or smaller.

In an exemplary embodiment, LEE 130 represents a light-emitting elementsuch as an LED or a laser, but other embodiments of the inventionfeature one or more semiconductor dies with different or additionalfunctionality, e.g., processors, sensors, detectors, control elements,and the like. Non-LEE dies may or may not be bonded as described herein,and may have contact geometries differing from those of the LEEs;moreover, they may or may not have semiconductor layers disposed over asubstrate as discussed below. LEE 130 may be composed of one or morelayers, for example semiconductor layers formed over a substrate. Thesubstrate may, for example, include or consist essentially of one ormore semiconductor materials, e.g., silicon, GaAs, InP, GaN, and may bedoped or substantially undoped (e.g., not intentionally doped). In someembodiments, the substrate includes or consists essentially of sapphireor silicon carbide; however, the composition of the substrate is not alimitation of the present invention. The substrate may be substantiallytransparent to a wavelength of light emitted by the LEE 130. For alight-emitting element, the semiconductor layers may include first andsecond doped layers which preferably are doped with opposite polarities(i.e., one n-type doped and the other p-type doped). One or morelight-emitting layers e.g., or one or more quantum wells, may bedisposed between the first and second doped layers. Each of these layersmay include or consist essentially of one or more semiconductormaterials, e.g., silicon, InAs, AlAs, GaAs, InP, AlP, GaP, InSb, GaSb,AlSb, GaN, AlN, InN, and/or mixtures and alloys (e.g., ternary orquaternary, etc. alloys) thereof. In preferred embodiments, LEE 130 isan inorganic, rather than a polymeric or organic, device.

In some embodiments, substantially all or a portion the substrate isremoved from LEE 130. Such removal may be performed by, e.g., chemicaletching, laser lift-off, mechanical grinding and/or chemical-mechanicalpolishing or the like. In some embodiments, all or a portion of thesubstrate is removed and a second substrate—e.g., one that istransparent to or reflective of a wavelength of light emitted by LEE130—is attached to the substrate or semiconductor layers prior to orafter the bonding of LEE 130 as described below. In some embodiments,the substrate includes or consists essentially of silicon and all or aportion of the silicon substrate may be removed prior to or after thebonding of LEE 130 to a conductive element or other system. Such removalmay be performed by, e.g., chemical etching, laser lift off, mechanicalgrinding and/or chemical-mechanical polishing or the like.

Electrical contact to LEE 130 may be achieved through contacts which maymake contact to the p- and n-layers respectively. LEE 130 may optionallyfeature a mirror or reflective surface formed over all or portions ofthe semiconductor layers and optionally other portions of LEE 130. Themirror may act to direct light emitted from the light emitting layerback towards and out the substrate, particularly in a flip-chipconfiguration, where LEE 130 is mounted contact-side down.

In some embodiments, the LEE 130 has a square shape, while in otherembodiments LEE 130 has a rectangular shape. In some preferredembodiments, to facilitate bonding) LEE 130 has a shape with a dimensionin one direction that exceeds a dimension in an orthogonal direction(e.g., a rectangular shape), and has an aspect ratio of the orthogonaldirections (length to width, in the case of a rectangular shape) of LEE130 greater than about 1.2:1. In some embodiments, LEE 130 has an aspectratio greater than about 2:1 or greater than 3:1. The shape and aspectratio are not critical to the present invention, however, and LEE 130may have any desired shape.

While the discussion herein has mentioned blue LEDs and phosphors, thatwhen combined produce white light, the concepts may be used with respectto LEDs emitting at any wavelength and phosphors orwavelength-conversion materials with any emission wavelengths that mayin combination or alone be used to produce any color.

The terms and expressions employed herein are used as terms andexpressions of description and not of limitation, and there is nointention, in the use of such terms and expressions, of excluding anyequivalents of the features shown and described or portions thereof. Inaddition, having described certain embodiments of the invention, it willbe apparent to those of ordinary skill in the art that other embodimentsincorporating the concepts disclosed herein may be used withoutdeparting from the spirit and scope of the invention. Accordingly, thedescribed embodiments are to be considered in all respects as onlyillustrative and not restrictive.

What is claimed is:
 1. A light-emitting device comprising: alight-emitting die having (i) a top face and a bottom face opposite thetop face, at least one of the top or bottom face being configured foremission of light therefrom, and (ii) a sidewall spanning the top andbottom faces; and at least partially surrounding the light-emitting die,a phosphor element comprising (i) a binder and (ii) disposed within thebinder, one or more wavelength-conversion materials for absorbing atleast a portion of light emitted from the light-emitting die andemitting converted light having a different wavelength, converted lightcombining with unconverted light emitted from the light-emitting die toform substantially white light, and a divergence of color temperature ofthe substantially white light emitted from the device varies, over anangular range of 0° to 85°, no more than 0.01 in terms of Δu′v′deviation from a spatially weighted averaged chromaticity, wherein thephosphor element has an outer contour having (i) a curved region thatdefines only a portion of a hemisphere having a hemisphere radius, (ii)a planar region (a) disposed over the light-emitting die, (b) having anon-zero z-offset within the hemisphere, and (c) substantially parallelto the top face of the light-emitting die, a ratio of the z-offset ofthe planar region within the hemisphere to the hemisphere radius havinga value ranging from 0.02 to 0.15, and (iii) a base opposite the planarregion having a non-zero centroid z-offset within the hemisphere, aratio of the centroid z-offset to the hemisphere radius having a valueranging from 0.3 to 0.8.
 2. The light-emitting device of claim 1,wherein the bottom face of the light-emitting die is substantiallycoplanar with the base of the phosphor element opposite the planarregion.
 3. The light-emitting device of claim 1, wherein the ratio ofthe z-offset of the planar region within the hemisphere to thehemisphere radius is a value ranging from 0.04 to 0.12.
 4. Thelight-emitting device of claim 1, wherein the outer contour of thephosphor element has a region defined by a cylindrical cutoff within thehemisphere.
 5. The light-emitting device of claim 4, wherein a ratio ofa length of the cylindrical cutoff to the hemisphere radius is a valueranging from 0.75 to 0.95.
 6. The light-emitting device of claim 5,wherein the length of the cylindrical cutoff is a value ranging from 50μm to 500 μm.
 7. The light-emitting device of claim 4, wherein a lengthof the cylindrical cutoff is a value ranging from about 0.2 mm to about20 mm.
 8. The light-emitting device of claim 1, wherein the hemisphereradius is a value ranging from about 0.5 mm to about 5 mm.
 9. Thelight-emitting device of claim 1, wherein (i) light emitted from thelight-emitting die has a Lambertian distribution and (ii) the convertedlight has an isotropic distribution.
 10. The light-emitting device ofclaim 1, wherein the divergence of color temperature of thesubstantially white light emitted from the device varies, over anangular range of 0° to 85°, no more than 0.005 in terms of Δu′v′deviation from a spatially weighted averaged chromaticity.
 11. Thelight-emitting device of claim 1, wherein the one or more wavelengthconversion materials comprise one or more phosphor particles.
 12. Thelight-emitting device of claim 1, further comprising, disposed beneathat least one of (i) at least a portion of the light-emitting die or (ii)the phosphor element, a mounting surface reflective to at least one ofconverted light or unconverted light emitted by the light-emitting die.13. The light-emitting device of claim 12, wherein the mounting surfacehas a reflectivity to visible light of approximately 95% toapproximately 98%.
 14. The light-emitting device of claim 1, wherein atleast a portion of the outer contour of the phosphor element has asurface texture for reducing total internal reflection.
 15. Thelight-emitting device of claim 1, wherein the light-emitting die is abare light-emitting diode die.
 16. The light-emitting device of claim 1,wherein the light-emitting die comprises a GaN-based semiconductormaterial.
 17. The light-emitting device of claim 1, wherein thelight-emitting die emits blue or ultraviolet light.
 18. Thelight-emitting device of claim 1, wherein the hemisphere radius is avalue ranging from about 0.2 mm to about 20 mm.
 19. The light-emittingdevice of claim 1, wherein the ratio of the centroid z-offset to thehemisphere radius has a value ranging from 0.5 to 0.77.
 20. Thelight-emitting device of claim 1, wherein the ratio of the centroidz-offset to the hemisphere radius has a value ranging from 0.3 to 0.5.21. The light-emitting device of claim 1, wherein the planar region hasa radius having a value ranging from 50 μm to 1000 μm.
 22. Thelight-emitting device of claim 1, wherein the ratio of the z-offset ofthe planar region within the hemisphere to the hemisphere radius isapproximately defined by −1.9×F+0.67, where F is a ratio of the z-offsetvalue of the planar region within the hemisphere to the hemisphereradius.
 23. The light-emitting device of claim 1, wherein the z-offsetof the planar region within the hemisphere is approximately defined by1.41×R−0.8, where R is the hemisphere radius.
 24. The light-emittingdevice of claim 1, wherein (i) the phosphor element has a base radiushaving a value ranging from 0.6 mm and 1.0 mm, (ii) the planar regionhas a radius having a value ranging from about 0.15 mm to about 0.45 mm,and (iii) a height from a base of the phosphor element to the planarregion is a value ranging from about 0.15 mm to about 0.5 mm.
 25. Thelight-emitting device of claim 1, further comprising at least oneadditional light-emitting die at least partially surrounded by thephosphor element.
 26. The light-emitting device of claim 1, furthercomprising: a second light-emitting die having (i) a top face and abottom face opposite the top face, at least one of the top or bottomface being configured for emission of light therefrom, and (ii) asidewall spanning the top and bottom faces; and at least partiallysurrounding the second light-emitting die, a second phosphor elementcomprising (i) a binder and (ii) disposed within the binder, one or morewavelength-conversion materials for absorbing at least a portion oflight emitted from the second light-emitting die and emitting convertedlight having a different wavelength, converted light combining withunconverted light emitted from the second light-emitting die to formsubstantially white light, wherein the second phosphor element has anouter contour having (i) a curved region that defines only a portion ofa hemisphere having a hemisphere radius, (ii) a planar region (a)disposed over the light-emitting die, (b) having a non-zero z-offsetwithin the hemisphere, and (c) substantially parallel to the top face ofthe light-emitting die, a ratio of the z-offset of the planar regionwithin the hemisphere to the hemisphere radius having a value rangingfrom 0.02 to 0.15, and (iii) a base opposite the planar region having anon-zero centroid z-offset within the hemisphere, a ratio of thecentroid z-offset to the hemisphere radius having a value ranging from0.3 to 0.8.
 27. The light-emitting device of claim 26, wherein thephosphor element and the second phosphor element are separated by a webtherebetween, the web comprising the binder.
 28. The lightemitting-device of claim 1, further comprising a substrate having aplurality of conductive elements disposed thereon, wherein (i) thelight-emitting die has at least two contacts on the bottom face, and(ii) each contact on the bottom face is electrically coupled to adifferent conductive element on the substrate.
 29. The light-emittingdevice of claim 28, wherein each contact on the bottom face of thelight-emitting die is electrically coupled to a different conductiveelement via at least one of a conductive adhesive, an anisotropicconductive adhesive, a wire bond, or solder.
 30. A light-emitting devicecomprising: a light-emitting die having (i) a top face and a bottom faceopposite the top face, at least one of the top or bottom face beingconfigured for emission of light therefrom, and (ii) a sidewall spanningthe top and bottom faces; and at least partially surrounding thelight-emitting die, a phosphor element comprising (i) a binder and (ii)disposed within the binder, one or more wavelength-conversion materialsfor absorbing at least a portion of light emitted from thelight-emitting die and emitting converted light having a differentwavelength, converted light and unconverted light emitted by thelight-emitting die combining to form substantially white light, whereinthe phosphor element comprises (i) a first region having a sidewallsubstantially parallel to the sidewall of the light-emitting die and(ii) disposed over the first region, a second region having a topsurface defining a portion of an oblate ellipsoid described by theequation${{z(r)} = \frac{r^{2}}{R\left( {1 + \sqrt{1 - {\left( {1 + K} \right)\left( {r^{2}/R^{2}} \right)}}} \right)}},$where z is a height of the second region above a top surface of thelight-emitting die, r is a radius of the oblate ellipsoid, R isapproximately 2.38, and K is approximately 6.0.